Feed processing for nitrogen rejection unit

Abstract

A system comprising a stripping column and a nitrogen rejection unit wherein a significant portion of the feed to the nitrogen rejection unit is provided at an increased pressure thus reducing product compression requirements.

We claim: 
     
       1. Method for cryogenic processing of a feed containing nitrogen and methane comprising: (A) partially condensing a feed comprising nitrogen and methane to produce a first vapor and a first liquid;   (B) passing first liquid into a stripping column;   (C) partially condensing first vapor to produce a second vapor and a second liquid;   (D) passing second liquid into the stripping column;   (E) passing second vapor into a nitrogen rejection unit for separation into nitrogen-enriched and methane-enriched components;   (F) removing a stream of nitrogen-enriched component from the nitrogen rejection unit; and   (G) removing a stream of methane-enriched component from the nitrogen rejection unit.   
     
     
       2. The method of claim 1 wherein the second liquid is passed into the stripping column at a point higher than the point where first liquid is passed into the stripping column. 
     
     
       3. The method of claim 1 wherein the feed is divided into first and second portions and each of the first and second portions are partially condensed by indirect heat exchange with at least one of the nitrogen-enriched component stream, the methane-enriched component stream and liquid from the stripping column. 
     
     
       4. The method of claim 1 wherein the fluids passed into the stripping column are separated into methane-richer and nitrogen richer fractions, at least some of the methane-richer friction is recovered as product methane, and at least some of the nitrogen-richer fraction is passed into the nitrogen rejection unit. 
     
     
       5. The method of claim 1 wherein the first vapor is partially condensed, at least in part, by indirect heat exchange with the methane-enriched component stream. 
     
     
       6. The method of claim 1 the second vapor comprises about 50 percent of the total feed into the nitrogen rejection unit. 
     
     
       7. Apparatus for cryogenic processing of a feed containing nitrogen and methane comprising: (A) means to partially condense feed containing nitrogen and methane to produce a first vapor and a firs liquid;   (B) a stripping column ad means to pass first liquid into the stripping column;   (C) means to partially condense the first vapor to produce a second vapor and a second liquid;   (D) means to pass second liquid into the stripping column;   (E) a nitrogen rejection unit for producing nitrogen-enriched and methane-enriched components, and means to pass second vapor into the nitrogen rejection unit;   (F) means for removing a stream of nitrogen-enriched component from the nitrogen rejection unit; and   (G) means for removing a stream of methane-enriched component from the nitrogen rejection unit.   
     
     
       8. The apparatus of claim 7 wherein the means to pass second liquid into the stripping column communicates with the stripping column at a point higher than the point where first liquid is passed into the stripping column. 
     
     
       9. The apparatus of claim 7 further comprising means to pass fluid from the stripping column to the nitrogen rejection unit. 
     
     
       10. The apparatus of claim 7 further comprising means to recover fluid from the stripping column. 
     
     
       11. The apparatus of claim 7 further comprising means to recover fluid from the nitrogen rejection unit.